Fair Comparisons

Years ago, I built a specialized test box for QSC Audio Products; an ABX tester. At the time, I thought that box was one of the coolest things I'd ever built and I used it as carelessly as any kid ever abused a toy. Because I didn't want any arguments about noise or distortion in the signal path, I used insanely expensive relays for the low signal switching mechanism and because they are make-before-break and mercury-whetted, switching "artifacts" were minimal unless the products under test had significant DC offset. The contacts themselves were gold-plated silver and the cases were hermetically sealed.

The high output relays were also silver contact, gold-plated but they were considerably less sophisticated, since they had to be able to withstand several amps of switching current with high power amplifiers. Later, the company produced a commercial version of the ABX tester for sales representative use and that product has received a lot of comment (mostly uninformed) on the internet:

• www.qscaudio.com/support/library/manuals/abxman.pdf
• http://en.wikipedia.org/wiki/ABX_test
• http://home.provide.net/~djcarlst/abx_qsc.htm
• http://rinchoi.blogspot.com/2012/09/qsc-audio-abx-comparator.html
• http://www.avsforum.com/t/528546/the-qsc-abx-box

A friend, Rob Schlette, did a well-informed article about some software based ABX testers for TheProAudioFiles.com ), Audio Perception and ABX Testing, a while back and that's a pretty good place to start your own thoughts about the subject.

A few of us--Jake Swanson (S&M Audio), Aaron Hodgson (McNally Smith Record Lab Manager), and I--recently revitalized the ABX tester for use at McNally Smith College of Music. I haven't had a chance to mess with the new unit, but I'm sure it will raise eyebrows and piss off "professionals" every bit as much as did the original QSC product.